The present invention relates to a method and apparatus for quantitatively measuring a metal phase by X-ray diffractometry, and a method of producing a galvanized steel sheet by using the method and apparatus. Particularly, the present invention relates to a method and apparatus for accurately measuring the deposit amount of a metal phase contained in a galvanized layer, particularly a desired metal phase of not less than two metal phases contained a galvanized layer, in a nondestructive state, and a method of producing a galvanized steel sheet by using the method and apparatus.
The quality characteristics (pealing resistance in processing, corrosion resistance, and the like) of a plating containing alloy phases significantly vary depending upon the deposit amount of each of the alloy phases in a galvanized layer. Therefore, in order to produce a plated product of high quality, it is important to accurately measure the deposit amount of each of the phases and control production conditions such as heat treatment conditions, and the like.
A typical example of plated products having galvanized layers containing alloy phases is an alloyed hot-dip galvanized steel sheet comprising a galvanized layer containing several types of Fexe2x80x94Zn alloy phases. The alloyed hot-dip galvanized steel sheet is produced by heat-treating a hot-dip galvanized steel sheet to positively grow the Fexe2x80x94Zn alloy phases in the galvanized layer in order to improve the quality characteristics such as pealing resistance, weldability, corrosion resistance and adhesion of a coated film after coating, and the like. The Fexe2x80x94Zn alloy phases of the galvanized layer on the steel sheet contain a xcex41 phase as a main phase, and small amounts of xcex93 phase and xcex6 phase depending upon the extent of heat treatment. The quality characteristics of the alloyed hot-dip galvanized steel sheet are significantly affected by the deposit amounts of the xcex93 phase and xcex6 phase in the galvanized layer. Therefore, in order to produce the alloyed hot-dip galvanized steel sheet of high quality, it is important to control the heat treatment conditions, for example, the heating temperature or heating time, to constantly control the deposit amounts of the xcex93 phase and xcex6 phase to appropriate levels.
Methods of measuring the deposit amounts of metal phases contained in a galvanized layer of an alloyed hot-dip galvanized steel sheet by X-ray diffractometry have been disclosed.
An example of the conventional methods is the method disclosed in Japanese Unexamined Patent Publication No. 9-33455. In this method, the galvanized layer is irradiated with X-rays to determine the deposit amounts of the xcex93 phase and xcex6 phase of the alloyed hot-dip galvanized steel sheet by using the measured intensities of diffracted X-rays from the Fexe2x80x94Zn alloy phases, the previously measured intensities of diffracted X-rays from an alloyed hot-dip galvanized steel sheet having known deposit amounts of the xcex93 phase and xcex6 phase, and a theoretical intensity formula for diffracted X-rays, calculating the degree of alloying. By using the theoretical intensity formula for diffracted X-rays, the number of reference materials can be significantly decreased, as compared with a conventional method. However, the intensities of diffracted X-rays are the same as conventional values. Therefore, there is no resolution of the problem of deteriorating measurement accuracy when the obtained diffracted X-ray intensity is low.
On-line measurement of a running steel sheet, such as on-line measurement of a steel sheet in a surface treatment step, also has a problem in which accurate measurement is made impossible by the influence of vibration of the steel sheet. Namely, the distance between an X-ray diffraction position and a detection system varies with vibration of the steel sheet flowing on a line to influence the diffracted X-ray intensity. Since alloy phases having small deposit amounts, such as the xcex93 phase and xcex6 phase, show low diffracted X-ray intensity, the deposit amounts of these phases cannot be easily evaluated with high accuracy.
In the use of diffracted X-rays for a galvanized layer containing a plurality of metal phases, the occurrence frequency of superposition of other peaks is increased to make quantitative accurate analysis more difficult.
The on-line measurement in the surface treatment step requires feedback of measurement results within a short time. In this case, the time of detection by a scintillation counter cannot be extended to fail to increase the count number of diffracted X-rays, and thus the above problems become significant.
Although, in the invention of Japanese Unexamined Patent Publication No. 9-33455, the above problems are solved by setting the appropriate theoretical intensity formula, the fundamental problem of week diffracted X-ray intensity cannot be resolved.
Another example of the conventional methods is the method disclosed in Japanese Unexamined Patent Publication No. 5-45305. This method is a method of measuring the degree of alloying of a galvanized layer in which the degree of alloying of the galvanized layer is measured by using a ratio between two specified X-ray diffraction intensities of alloy phases. Also, the degree of alloying of the galvanized layer is measured by using a ratio of one specified X-ray diffraction intensity of alloy phases to background intensity. This method is aimed at measuring the degree of alloying of the galvanized layer with high accuracy in a practical alloying region. However, the detected X-ray diffraction intensity itself is not increased. Therefore, sufficient accuracy cannot be obtained according to the conditions of a measurement sample.
The above publications respectively disclose drawings schematically showing parallel beam optical system X-ray diffractometers used for the conventional techniques. However, these diffractometers have no characteristic as an apparatus.
In consideration of the above-described circumstances, an object of the present invention is to increase diffracted X-ray intensity from a metal phase contained in a galvanized layer to improve the measurement accuracy of the deposit amount of the metal phase contained in the galvanized layer. Another object of the present invention is to contribute to the production of a galvanized product of high quality. A further object of the present invention is to provide a measuring apparatus and method capable of accurately measuring the deposit amount of an alloy phase even when the distance between an X-ray diffraction position and a detection system varies with vibration of a steel sheet, like in on-line measurement of a running steel sheet.
In order to improve the measurement accuracy of minor components by X-ray diffractometry, the inventors selected the method of increasing the detected X-ray diffraction intensity itself as a drastic measure. The detected X-ray diffraction intensity itself was increased to achieve a method and apparatus for accurately quantitatively determining minor components of the present invention. Particularly, the inventors invented a method and apparatus for acculately quantitatively determining the degree of alloying of a galvanized layer of a metal.
In order to increase the detected X-ray diffraction intensity itself, a detector capable of detecting larger quantities of diffracted X-rays than a conventional detector was designed. In another device, the parallelism of the produced X-rays is improved to decrease diverging X-rays, thereby increasing diffracted X-ray intensity, as compared with a conventional method. The present invention relates to these methods and an apparatus for realizing the methods, and a method of producing a galvanized steel sheet by using the methods and apparatus.
The present invention provides a method and apparatus for measuring the deposit amount of a metal phase contained in a galvanized layer by X-ray diffractometry, the method comprising measuring diffracted X-rays from the metal phase contained in the galvanized layer over a predetermined range on a Debye ring, and integrating the obtained X-ray diffraction intensity data to permit the accurate measurement of the deposit amount of the metal phase.
The present invention also provides a method of measuring the deposit amount of a metal phase contained in a galvanized layer by X-ray diffractometry, the method comprising measuring diffracted X-rays from the metal phase at a plurality of positions on at least one Debye ring formed by the diffracted X-rays to detect large quantities of X-rays, and integrating the obtained X-ray diffraction intensity data to increase the X-ray intensity data, thereby permitting the accurate measurement of the deposit amount of the metal phase.
As the metal phase, a single phase or a plurality of phases may be used, and when the metal phase is either a pure metal phase or an alloy phase, accurate measurement is possible. More specifically, the present invention is preferably applied to the case in which plating is hot-dip galvanization or alloying hot-dip galvanization.
Furthermore, the measuring method of the present invention can be performed in the step of treating the surface of a steel sheet to permit accurate on-line measurement of the deposit amount of the metal phase contained in the galvanized layer. The results of measurement can be used for controlling alloying conditions.
The present invention further provides an apparatus for measuring the deposit amount of a metal phase in a galvanized layer by using the above-described method, the apparatus comprising an X-ray source for irradiating the galvanized layer containing the metal phase with an X-ray beam, a detector for detecting diffracted X-rays from the metal phase contained in the galvanized layer over a predetermined range along a Debye ring, and a data processing device for processing data of the X-ray intensity detected by the detector. The detector has an X-ray detection surface curved along the Debye ring. The detector may be a scintillation counter having the function to scan the predetermined range along the Debye ring.
The present invention further provides an apparatus for measuring the deposit amount of a metal phase in a galvanized layer, comprising an X-ray source emitting an X-ray beam, a plurality of X-ray detectors disposed on at least one Debye ring of diffracted X-rays produced from a material irradiated with the X-rays, for detecting diffracted X-rays, and an integrating meter for integrating the diffracted X-ray intensity data obtained by the X-ray detectors for at least one Debye ring.
The present invention further provides an apparatus for measuring the deposit amount of an alloy phase in a galvanized layer on a steel sheet by using X-ray diffractometry, the apparatus comprising X-ray radiation means comprising an X-ray source emitting an X-ray beam, a multilayer film mirror for compressing the emitted X-rays and making the emitted X-rays monochromatic and parallel, and a slit for transmitting a portion of the parallel X-rays, and X-ray detection means for detecting diffracted X-rays from a measurement material contained in the galvanized layer on the surface of the steel sheet irradiated with the X-rays.
In the method of measuring the deposit amount of an alloy phase contained in a galvanized layer on a steel sheet by X-ray diffractometry, in X-ray irradiation of the measurement material contained in the galvanized layer on the surface of the steel sheet, the X-ray beam produced by the X-ray source is made parallel by using the multilayer film mirror to permit accurate measurement of the deposit amount of the alloy phase in the galvanized layer on the steel sheet.
In the method and apparatus of the present invention, the detected X-ray intensity (total amount of X-rays detected per unit time) can be increased to improve the accuracy of measurement of the deposit amount of the metal phase.